Photometer.



No.'7|2,397. 4 I Patented oor. 28, |902.

P; MATTHEWS.

PHTUMETER.

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No. 7I2',397. Patented Oct. 28, 1902.

C. P, MATTHEWS.

Pnuomeg. (Appligtionled Mar. 24, 1902) (No Model.) 3 Sheeis'-Sheet 2.

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Patented-Oct. 28, |902. -C."P.F MATTHEWS.

Puoomsre. @Application mea Mar. 24. 1902.)

(No Model.)

- QC.. F. MATTHEWS i Io Vlxufnnl) STATE *PATENT Ormes.

CHARLES PHILO MATTHEWS, OF LAFAYETTE, INDIANA, ASSIGNOR TO LOUIS B. MARKS, OFiNEW YORK, N; Y.

PHoToMETt-:a

SPECIFICATION forming' part of Letters Patent No. 712,397, dated October 28, 1,902. Application filed March 24, 1902. Serial No. 99,743. (Ne model.)

To afZZ whom, t may concern:

Be it known that I, CHARLES PHILo MAT- THEWS, a citizen ofthe United States of America,and a resident of Lafayette, in the county of Tippecanoe and State of Indiana, have invented certain new and useful Improvements in Photometers, of which the following is a specification. y

My present invention relatesin general to photometers, and in particular toan Ainstru-i ment adapted to indicate thefmean spherical linear direction, Vas in ordinaryphotometers,. and without altering the construction. Only` some small adjustments are necessary for". changing the apparatus from one type of pho.`

tometer to the other;

By av slight manipulation my invention is"` adapted to the direct measurementof the rcduction-factor or the ratio of the mean spherical candle-power to the mean horizontal candle-power. j y

Without setting forth the exact novelty ot' the invention, which is attended to in the claims, I may state generally that the nature of the organization coinprisingthe invention consists in a series of mirrors so arranged in accordance With mathematical and scientific, principles of light as to illuminate one side` of a screen proportionally to the mean spherical or hemispherical candle-power ot the source to be tested, said source of light preferably being rapidly rotated or spun ou its axis. nated by rays reflected from mirrors, which receive light from the standard sourceonly, an opaque screen being located between` the two sources of light., In principle it is immaterial whether the standard light or the last-named mirrors are moved until the illu- `The other side of the screen is illu mi- `ured by a given size of apparatus.

mination of the photometer-screen on the respective sides is balanced; but the particular construction illustrated herein is based upon the adj ustability of said mirrors. The aforementioned mirrors in aseries are arranged circularly, according to a certain law, and after once being adjusted remain fixed for all ordinary intensities of light adapted to -be meas- The rays `from the spinning lamp-as, for example, an

incandescent electric lamp and radiating in the plane of the axis of rotation-are directed by mirrors arranged in a semicircle around the center of the source of light, and the reiiected rays' are finally brought all upon one sideof a photometer-screen. Another result ofthe arrangement of mirrors `is the reduction ofthe intensity of each ray or-pencil in the ratio of the cosine of theangle to the normal to` one. The ray incident upon the pho- Ftomet'er-screen at a certain angle to the nor- Amal is reduced in candle-power approximately 'in the ratio of the cosine of that angle to one. Inasm uch as this cosine law is not exact the mirrors are so disposed as to compensate for Vthe difference, and this is accomplished by adjusting and then xing the mirrors nearer the screen than if the cosine law were exact.

` More generally stated, my invention is for measuring the mean spherical or hemispherical candle-power; and it consists of a fixed standard light, a support for a fixed source of light to be tested and cutoff from the standard light as to illumination, a iixed photometerA-screen cut olf from said lights as to direct illumination, devices movable to and from said screen in the path of the rays of light radiated from said standard light and directed upon one side of said screen, and deviceslike the above-named devices, only ixed, located in the pat-h of the rays radiated from said source and directed to the other side of said screen and located, respectively, at different angleswith regard `to the n'ormalof said screen and at predetermined distances therefrom.

My invention consists also of a photometerscreen, a lixed standard light,fa support for a xed source of light to be tested, au opaque screen between the two lights, and relatively IOO movable mirrors for throwing the light from the respective sources upon the photometer- SCI'eeIl.

All the details of my apparatus in so far as my invention is concerned are set forth in the accompanying drawings.

Figure lis a side elevation of the whole apparatus in outline. It may be considered as a diagram, as the exact mechanical construction in all its details is immaterial to the iuvention. Fig.2 is a plan of substantially all that is shown in Fig. l. Fig. 3 is intended to be a diagram to show especially the paths of the rays of light and so many of the mechanical elements as are necessary for tracing the rays. The view is perspective. Fig. 4 isaplan of that portion of the apparatus which serves for horizontal measurements of candlepower. Fig. 5 is a sidel elevation of what is shown in Fig. 4.

The apparatus consists of the combination of a photometer-screen P standing in a vertical plane, a source of light S to be tested on a support or pulley p, wit-l1 its center in an extension of said plane and on the same level as the central portion of said screen, a standard light S' back of said source on a support p and separated by an opaque screen o from the light S and located on the same level with said light and with said photometer-screen, a pulley p and belt B, by which the light S may be spun, a fixed photometer P, in which is located the photometer-screen P and which is provided with a telescopic eyepiece T (which, however, is not an element. of the invention) for viewing the screen, a bar R, providedvwith a pinion p" for feeding the bar to and fro in a' direction perpendicular to the plane of the screen and centrally located between the light S and the photom'eter-screen P, aA pair of mirrors M3 M4, carried at the left-hand end of the bar, a pair of mirrors M and M2, carried at but removable from the right-hand end of the bar R, the mirrors being all of the same reflecting-power and suitably cut from one piece of glass for eliminating the coefficient of absorption ot` the mirror, the planes of the mirrors being vertical and each mirror standing at forty-five degrees to an opaque screen O,which stands vertical above the bar R, midway between the central portion of the photometer-screen and the lightS and perpendicular to the plane of the photometer-screen, the mirrors M', M2, M3, and M4 all being at the same level with one another, the arrangement being such that a ray from the `light S will be reilected atforty-tive degrees from the mirror M2, then at forty-tive degrees from the mirror M', and will then strike the photometer-screen at a right angle and so that a ray from the standard S will travel in a similar manner with respect to the mirrors M4 and M3 perpendicularly to the photometerlP. Pairs of mirrors m m2 and m3 m4, &c., similar to the pair M/ M2, except that the former pairs are located at equal intervals of ifteen degrees around a semicircle f plication of the cosine la`w.

both above and below the pair M and M2, the mirrors of each pair standing at right angles to each other and each mirror of each pair standing at an angle of forty-five degrees to a vertical plane and on opposite sides thereof, and all the pairs, eleven in number, eX- cept the pairM3 M4, being at the right ot' the photometer-screen P, the distances ot' the pairs which are in the semicircle from the center of the circle being derived and determined from calculation, once for all, from the cosine law, and then set in toward the center to correct the inaccuracy of said law.

In the diagram in Fig. 3 lines represent rays and points represent mirrors. For example,

m 'm2 are the mirrors or the central points of the mirrors. m l m' 2 illustrates the positions of the mirrors as determined-by an apthat these mirrors have been moved equallytoward the center in order to secure the right position, and so with vthe other pairs, which` are all moved to and then fixed at locations near the center of the circle. 4f"

The terms ,horizontalf ve,rtical,"1evel,

dce., of course are only relative and usedfor convenience in explaining what,V is shown in the drawings; but the Whole apparatus may be turned upside down or at any angle, so

that nothing need necessarily be vertical orV horizontal.

Experiment and calculation show that eleven pairs of mirrors at intervals of fifteen degrees are sufficient to insure an accuracy within .6 per cent., the efect being asfif there were eleven sources of light arranged in the position where the images would seem to be if the mirrors were looked into by an observer at the photometer-screen P. Some of the images are indicated at 0c y' z. More mirrors would insure greateraccuracy; but .6 per cent.

is within the limits of observational error,. and hence a greater number is unnecessary.

m and m2 show.

IOO

IIO

series of twenty-two mirrors. Theyremain fixed, and so do the others inthe semicircle, during the whole operation of measuring lights of the same or different candle-powers, provided the mean spherical 'candle-powers are to be determined. If the operator should place his eye in a'position of the photometerscreen P, he would see eleven images, and each image would shed light upon the photometer-screen at an angle determined `by the elevation or depression of the mirrors to which such image is due, this inclined incidence ot' the light andthe apparent distance of theimages producing together the required reduction in the illumination, so that the 'total4 illumination of one side t' photometer-screen is proportional to the mean spherical intensity of the source to be tested. The next IZO claims,` i i My .apparatus mayalso serve for the direct stepconsists in turning the pinion p `until the mirrors MiandM r'eiiect` enoughlight from the standard S to balance the illumination of the screen. lf a stronger source of light is to be tested, the pair of` mirrors M3 M4 would, on the principle` of inverse squares,` have to "be moved nearer the photometerscreen. In order to measure the mean hemispherical intensity of the source either above 1 My invention `is broad enough for permit-` ting aivariation in the number of mirrors employed oranyother change` covered' by the measurementof the mean spherical reduction factor Aor the mean spherical candle-power dividediby the mean horizontal candle-power. Remove the' opaque screen 0 and the standard lamp. Now the right-handside of the screen is illuminated proportionally to the mean spherical `candle-power of the single source of light, or,inother words, the mean spherical candle-power is measured against' the mean horizontal candle-power, and hence the mean spherical reduction factor becomes known directly. i Y

The lamp S may be rotated by means of the belt B. The object of rotating the lamp is for radiating the same average of lightl to the mirrors 'which arearrangedin `the circle, the lamp consisting usually of a lament, which is apt to radiate more light in one direction than in another.Y i

I claim as my' inventionu `l.` Apparatus for measuring candle-power, consisting of the `combination of a photometer-screen, supports for sources of light,fand different devices for receiving and directing the 'light from the sourcesto said screen ina predetermined manneigone of said devices being movable' to and fro with respect to both said screen andsaid lights.

2.1 Apparatus't'or measuring candle-power, consistingof the combination of a photometer-screen, a standard light, a support for a source of light to be tested, an opaque screen between the two lights, and two pairsof mirrors forthrowing the light from therespecl tive sources upon said 'photometer-screen, one pair of mirrors`,and screens beingrelatively movable forilluminating the photometer-screen` in a predetermined manner', `ou`e pair of mirrors serving to reflect. the rays,` from one light to said `photom eter-screen, and

" tive devices.

the other pair serving to retlect the rays from the" other light to saidphotometer-screen.

3. Apparatus for measuring candle-power, consisting of the combination of a` photometer-screen, a fixed standard light, a support for a ixed source of light to `be tested, an opaque screen between the two lights, a pair of mirrors for receiving and reflecting the light from the standard to said screen, and movable to and fro with respect to said screen, and another pair of fixed mirrors for receiving and reflecting the light from said source to be tested, to said screen.

4. Apparatus for measuring candle-power, consisting of the combination of a `photometer-screen, supports for sources of light, means for receiving and i directing the light from the sources to opposite sides of said screen, and a device for causing a relative displacement of said means from said photometer-screen, a portion of said means consisting of pairs of mirrors in the path of the rays from one of said sources, and the remainder of said means consisting of a single pair of mirrors in the path of the rays from the other source of light.

i `5. `Apparatus for measuring candle-power, consisting of the combination of supports for sources of light cut off from each other as to mutual illumination, aphotometer-screen cut olf from said lights as to direct illumination, devices located at a distance from said lights land` from said screen for receiving the rays `and returning the same to Iopposite sides of said screen, and a bar connecting said devices `and movable to and fro, for varying the dis- ;tances between said screen and the respec- 6.` Apparatus for measuring candle-power,

screen cnt off from said lights as to direct illumination, devices located at a distance from said lights and from said screen for receiving the rays and returning the same to opposite sides of said screen, a bar connecting said devices and movable to and fro, for varying the distancebetween said screen andthe re-` spective devices, and mechanism for moving; said bar.

"7.` Apparatus for measuring candle-power,

`consisting of the combinationof supports for ifixed sources of light cut olf from each other las to mutual illumination, a photometersides of said screen, and means for varyingA the respective distances between said screen and said mirrors.

I 8. Apparatus for measuring candle-power, consisting of the combination `of supports for fixed sources of light cutoi from each other i IOO consisting of the Vcombination of. supports A ffor sources of rays of light cut o from each` 'other as to mutual illumination, a photometer- IIO as to mutual illumination, a fixed photometer- Y screencut ott from the lights as to direct illu- A mination, mirrors in pairs locatedvat a distance from said lights and from said screen and on opposite sides thereof and standing individually at forty-five degrees to the plane of said screen and to the direction of said mirrors, andmeans for moving either pair nearerto and simultaneously the other pair of mirrors farther from'said screen ina perpendicular direction to said screen.

9. Apparatus for measuring candle-power, consisting of the combination of supports for fixed sources of light cut oft fromeach other as to mutual illumination, a 'xed photometerscreen cut olf from said lights as to direct illumination, a pair of mirrors on one side of the screen, movable to and from the screen, individually standing at forty-five degrees to the plane of said screen and located in the path of the ray of light from one of said sources to one side of said screen, and fixed pairs of mirrors arranged in series inv a semicircle approximately and located in the path of the rays from the other source to the other Vside of said screen, and located at predetermined distances from said screen, the axis of said circle being in a line lying in the plane of said screen and passing through the cen ter of the last-named source of light.

10. Apparatus for measuring candle-power, consisting of the combination of a fixed standard light, a support for a xed source of light to be tested cut oft from the standard light as to illumination, a 'xed photometer-screen cut o from said lights as to direct illumination, movable mirrors in the path of the rays of light emanating from said standard light and reiiected upon one side of said screen, and fixed mirrors located in the paths of rays of light radiated from said source and reflected to the other side of said screen, and located respectively at dierent angles with regard to the normal of said screen and at predetermined distances from said screen.

1l. Apparatusformeasuringcandle-power, consisting of the combination of a fixed standard light, a support for a fixed source of light to be tested and cut off from the standard light as to illumination, a iixed photometerscreen cut o from said lights as to direct illumination, devices movable to and from said screen in the path of the rays of light radiated from said standard light and directed upon one sideof said screen, and devices like the above named devices, only fixed, located in the path of the rays radiated from said source and directed to the other side of said screen, and located respectively at different angles with regard to the normal of said screen, and at predetermined distances therefrom.

12. Apparatus for measuring candle-power, consisting of the combination of a fixed standard light, a support for a fixed source of light to be tested cut ed from the standard as to illumination, a fixed photometer-screen cut o from said lights as to direct illumination, a movable device for receiving light from said standaidand directing it upon one side of saidnscreen, and other devices like therstnamed, located at intervals inV acircle approximately drawn about the screen with a predetermined radius, for respectively receiving different rays from said source, and directing them to the other side of said screen. 13. Apparatus for measuring candle-power, consisting ofthe combination of a fixed standard light, a support for a iixed source of light to be tested cutoff from the standard as to illumination, a fixed photometer-screen cut 0E from said lightsy as to direct-illumination, a movable reliecting medium for receiving rays from said standard and directing them upon one side of said screen, and other reflecting mediums located at equal intervals circularly approximately at predetermined distances from said screen, for respectively receiving different rays from said source and reflecting them tothe other side of said screen.

14. Apparatus for measuring candle-power, consisting of the combination of a standard light, a spinning support for a source of light to be tested cut off from the standard as to illumination, a photometer screen cut oft from said lights as to direct illumination, a reflecting medium for receiving rays from said standard and directing them upon one side of said screen, and other reflecting mediums at predetermined distances from said screen, for respectively receiving different rays from said source and reflecting them to the other side of said screen, and means for causing a balance of the illuminations on the two sides of said screen.

15. In an apparatus for measuring candlepower, the'combination with the support for the light to be tested, of a photometer-screen, and mirrors so fixed, as to illuminate said screen proportionally to the mean spherical candle-power of said light,'said mirrors remaining stationary during the operation of measuring the light.

16. In an apparatus for measuring candlepower, the combination with the support for the light to be tested, of a photometer-screen, and devices so ixed, as to illuminate said screen proportionally to the mean spherical candle-power of said light.

17. In an apparatus for measuring candlepower, the combination of a support for the source of light to be tested, a photometerscreen cut od from said source as to direct illumination, movable mirrors in the path ot' the rays of light radiated from one side of said light and reflected from said mirrors upon one side of `said screen, and ixed mirrors located in the paths of the rays of light radiated from the other side of said source, and reiiected by said fixed mirrors upon the other side of said screen, and located angularly about said source and said screen.

18. Apparatus for measuring candle-power, consisting of the combination of a support for a fixed source of light, a fixed photometerscreen cut oi from said light as to direct illu- IOO IIO

mination, a pair of mirrors on one side of the screen, movable to and from the screen, individually standing at forty-tive degrees to 4the plane of said screen and located in the path of the rayot"` light from said vsource to one side of said screen, and fixed pairs of mirrors arranged in series in a semicircleapproximately and located in the path of the rays from the source to the other side of said screen, and `located at predetermined distances from said screen, the axisof said circle being in a line lying in the plane oi' said screen and passing through the center of the source of light.

19. Apparatus for measuring candle-power, consisting of the combination of a support for a fixed source of light to be tested, a fixed photometer-screen cut ott from said light as to direct illumination, a movable device for receiving light from said source and directing it upon one side of said screen, and other de vices like the first named, located at intervals in a circle approximately drawn about the screen with a predetermined radius, for4 respectively receiving dierent rays from said source, and directing them to the other side of said screen. v l i 20. Apparatus for measuring candle-power, consisting of the combination of asupport for a flXed source of light to be tested, a fixed Photometer-screen cut oft from said light as to direct illumination, devices movable to and from said screen in the path of the rays of light radiated from said source of 'light and directed upon one side of said screen,and devices like the above named devices, only lxed, located in the path of the rays radiated from said source and directed to the other side of said screen, and located respectively at different angles with regard to the 2l. Apparatus for measuring candle-power, consisting of the combination of a support for a tixed source of light to be tested, a iXed `photometer-screen cut olf from said light as to .direct illumination, a movable reflecting to"` direct illumination, a reiiecting medium for receiving rays from said source and directinglhem upon oneside of` said screen, and other -reflecting mediums arranged in a curved path around and at predetermined distances from said screen, for respectively receiving different rays from said source andreiiecting them to the other side `of said screen, and means for causing a balance of the illumination on the twosides of said screen.

23. In apparatus for measuring candle power, the combination with the support for the sourceof light to be tested, of a photometer-screen, and devices so located as to illuminate one side of said screen proportionally.

to the mean spherical candle-power, and the other side proportionally to the mean horizontal candle-power, for the purpose as set forth, ofthe direct measurement of the mean spherical reduction factor.

Signed this 18th day of March, 1902.

CHARLES PHILO MATTHEWS. IIL. s] Witnessesz J. W. MCCREA, C. C. PYKE. 

